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Pii: s1062-1458(01)00427-5

zone, algorithms to discriminate supraventricular tachycar- dia (SVT) from VT may be activated. Even with the inclu-sion of atrial intracardiac electrograms in SVT discrimina- My Defibrillator Fired: What to Do?
tion algorithms, 20% or more of ICD therapies areinappropriate (Figure 1). ICDs also incorporate sophisti-cated information storage and diagnostic capabilities, Henry F. Clemo, MD, PhD, FACC, Kenneth A.
which may be noninvasively accessed using an ICD pro- Ellenbogen, MD, FACC, Medical College of Virginia, grammer and are immensely helpful in the work-up and Virginia Commonwealth University, Richmond, treatment of an ICD patient who has had a shock. For example, stored intracardiac electrograms and event logsallow the physician to determine the type of arrhythmiaprecipitating device therapy. Diagnostic data may give clues The management of a patient whose implantable cardio- to the presence of a conductor fracture or insulation failure, verter-defibrillator (ICD) has just fired has become a com- which could lead to inappropriate therapy.
mon problem for the non-electrophysiologist. The ICDpatient who has just received device therapy is often fright-ened and his cardiologist may feel unprepared to deal with Diagnostic Approach to the ICD Patient Who Has
this type of patient. Management of the ICD patient requires Had a Shock
a basic knowledge of indications for ICDs, function of ICDs, The approach to the ICD patient who has had therapy diagnostic approach to the patient whose ICD has fired and should include a directed history and physical, a diagnostic specific treatment guidelines for common triggers of ICD evaluation, and device interrogation. A systematic approach will help the physician to rapidly triage the patient and This review will focus on the latter two points outlined initiate treatment if necessary.
above. The reader is directed to the American Heart Asso-ciation/American College of Cardiology guidelines for ICD History and Physical
indications and to several recent comprehensive reviews Initial questioning of the patient should cover the points about ICDs for further information provided in the Sug- included in Table 1. Multiple episodes of ICD therapy in a gested Reading section.
short period of time should be viewed as a medical emer- The Function of ICDs
gency and the patient should be rapidly transferred to thehospital emergency department for immediate electrocar- The ICD system is composed of a pulse generator and one diographic monitoring to document arrhythmias and fur- or more leads or patches capable of sensing, pacing and ther work-up. Multiple ICD discharges may be the result of defibrillation. The generator is comprised of a battery, high- a fractured lead or recurrent VT/VF (electrical storm). If the voltage capacitors and electronic circuitry responsible for patient had only an isolated shock and otherwise feels well, tachyarrhythmia detection, therapy delivery, bradyarrhyth- semielective follow-up can be arranged. If the patient had mia pacing, diagnostics and telemetry. The lead and/or chest pain, shortness of breath or syncope associated with patch system can either be epicardial with ventricular sens- one or more shocks, he should be urgently evaluated since ing/pacing leads and defibrillation patches or an integrated an unstable acute cardiac syndrome may be present. Drug transvenous, endocardial defibrillation, sensing/pacing lead history is important, since some medications may be proar- system. Earlier ICDs were quite large, requiring implanta- rhythmic, or the discontinuation of antiarrhythmic medica- tion of the pulse generator in the patient's abdomen either tions may predispose the patient to arrhythmias such as above or below the rectus muscle. In the past decade, ICDs atrial fibrillation or VT. A history of trauma to the ICD have evolved to encompass a transvenous single or dual coil system should be elicited, since a lead fracture may be sensing/defibrillation lead placed via a central vein (e.g., causing inappropriate noise and triggering therapy. Multi- cephalic, axillary or subclavian vein) in conjunction with a ple firings of a recently implanted ICD system may be small pectorally implanted pulse generator (⬍40 cm3, caused by lead dislodgement.
⬍80 g). Other recent additions to the capabilities of ICDs The initial physical exam should be directed to the include advanced dual chamber bradycardia pacing, thera- cardiovascular and respiratory systems, looking for triggers pies for atrial tachyarrhythmias, and biventricular pacing, of SVT or VT/VF including cardiac ischemia, congestive which may have a beneficial effect in heart failure patients.
heart failure or hypotension. Infection or pulmonary dis- The primary detection parameter for ventricular tachy- ease exacerbation are other important triggers of tachyar- cardia (VT) or ventricular fibrillation (VF) is the ventricular rhythmias. The ICD site should be carefully examined for rate. Many ICDs have a VT zone (typically 150 –200 bpm) evidence of trauma. If lead fracture is suspected, further and a VF zone (typically ⬎200 bpm). A programmable examination (preferably done when the ICD is inactivated minimum number of ventricular intervals faster than the and intracardiac electrograms can be monitored) may in- rate cutoff must be exceeded to trigger therapy. In the VT clude flexion/extension of the arm ipsilateral to the side of ACC CURRENT JOURNAL REVIEW Sep/Oct 2001 2001 by the American College of Cardiology Published by Elsevier Science Inc.
Figure 1. Atrial fibrillation with a rapid ventricular response leading to inappropriate therapy, as recorded by a dual chamber pacing, ventricular defibrillator. The stored atrial
electrogram (top tracing) shows atrial fibrillation. The corresponding stored ventricular electrogram as recorded by the tip to the defibrillation coil of the ventricular leadwhich is in the right ventricle (RV Tip - RV Coil, middle tracing) and by the right ventricular coil to superior vena cava coil of the ventricular lead (RV Coil - SVC Coil,lower tracing) demonstrates a rapid ventricular response. Programmed SVT discriminators initially suppressed therapy but eventually a sustained high ventricular rateduration was exceeded leading to inappropriate therapy.
the ICD implant, isometric pushing or pulling of the arms, Treatment of the Patient with ICD Shocks
Valsalva maneuvers and bending.
If the patient has received only an isolated shock and has no The underlying cardiac rhythm should be documented.
residual symptoms, telephonic assessment and reassurance Supraventricular tachycardias including atrial fibrillation is often all that is needed. The patient can be followed up at are common triggers of inappropriate ICD therapy. Non- his next ICD clinic visit when the ICD can be interrogated.
sustained ventricular ectopy may suggest recurrent ventric- The patient should be advised to seek earlier medical eval- ular arrhythmias causing appropriate discharge.
uation if he has additional shocks. Obviously, if the patient Initial blood work should include serum potassium and has lingering symptoms as mentioned previously, he magnesium levels since hypokalemia and hypomagnesemia should seek urgent medical attention.
are important triggers of SVT and VT. Other blood workshould be directed to underlying diseases (i.e., hypoglyce- mia in a diabetic patient or anemia in a patient with a recent The patient who presents with multiple ICD shocks should blood loss may trigger sinus tachycardia). If an acute cardiac be treated as a medical emergency. Multiple shocks are syndrome is suspected, markers of myocardial infarction painful and frightening to the patient and may cause signif- should be determined.
icant psychological dysfunction. To decrease anxiety, the A chest radiograph should be obtained if lead fracture or ICD patient who has received multiple shocks should be lead dislodgment is suspected. Other imaging should be based on concurrent pathological processes.
In the case of multiple shocks, the ICD should be promptly inactivated. Concurrently, the patient should be monitored on telemetry and external defibrillation should Present ICDs store a wealth of diagnostic information in- be readily available. Ideally, the ICD should be inactivated cluding cardiac electrograms at the time of ICD discharge.
using a programmer. Often, this cannot be done because a Early ICD interrogation is indicated so that the triggering programmer may not be readily available, the manufacturer arrhythmia can be determined. Other diagnostic informa- and model of ICD may be unknown, or the health care tion can help determine if a lead fracture is present. This provider caring for the patient may be unfamiliar with the information can be printed and faxed to a clinical cardiac programmer. For most ICDs, tachyarrhythmia therapies electrophysiologist who can provide initial telephone guid- may be temporarily inactivated by taping a doughnut- ance to the treating physician. All ICD companies in the shaped magnet in place over the ICD. This is dependent on United States maintain a technical workforce of experts whether the ICD has been programmed to ignore magnet who are available to help with interrogation and interpre- application (feature in CPI/Guidant, Intermedics and Ven- tation of ICD information.
tritex/St. Jude ICDs). Application of a magnet to some ICDs ACC CURRENT JOURNAL REVIEW Sep/Oct 2001 Table 1. Pertinent Clinical Information Concerning ICD Firing
After initial patient stabilization, the ICD should be promptly interrogated. A flow diagram for evaluating and Irregular (atrial fibrillation) treating ICD discharges based on the ICD interrogation is Regular (SVT vs. VT) shown in Figure 2.
Preceding symptoms? Shortness of breath (CHF exacerbation)Chest pain (cardiac ischemia) Dizziness or loss of consciousness (hemodynamically destabilizing In the case of electrical storm (multiple episodes of VT/VF Recent changes in medications? causing device therapy), standard Advanced Cardiac Life Addition of diuretic (hypokalemia precipitating AFIB or SVT) Saving (ACLS) protocols should be followed for cardiovas- Addition of antiarrhythmic or other agent (proarrhythmia) cular and respiratory support. Since recent studies have doc- Discontinuation of a beta-blocker or other negative chronotropic agent (sinus umented the efficacy of beta-blockers in electrical storm and Recent reprogramming of ICD the superiority of intravenous amiodarone over lidocaine in Lowering of VT rate threshold (inappropriate detection of SVT) the treatment of refractory, unstable VT/VF, these agents Change in SVT discriminators (inappropriate detection of SVT) should be first line therapy for suppression of VT or VF. Other Activity When ICD Fired precipitating causes of VT/VF should be treated, including Physical activity (sinus tachycardia trigger)Upper extremity movement (lead fracture) hypokalemia and hypomagnesemia, cardiac ischemia, hyp- Exposure to electromagnetic interference (electrocautery, alternators, anti- oxia, congestive heart failure or cardiogenic shock.
theft devices, etc.) Chronic antiarrhythmic therapy for suppression of VT/VF Frequency of ICD Firing may include amiodarone, or sotalol, both of which decrease Multiple episodes in previous 24 hours (lead fracture, SVT, electrical storm)Infrequent episodes with symptoms similar to past occasions (isolated VT/VF the frequency of ICD discharges. Other therapies which sup- press sudden cardiac death including beta-blockers, angioten- sin converting enzyme inhibitors, lipid lowering agents and Congestive heart failure (exacerbation could lead to VT or SVT) spironolactone should be included when appropriate. Coro- Coronary artery disease (recent ischemia could precipitate VT or SVT)Hypertension (changes in diuretic could lead to hypokalemia and VT or SVT) nary artery revascularization may be indicated if the patienthas significant cardiac ischemia. If the patient has recurrent VT Abbreviations: AFIB, atrial fibrillation; CHF, congestive heart failure; ICD, implant- able cardioverter-defibrillator; SVT, supraventricular tachycardia; VF, ventric- ⬍200 bpm, aggressive overdrive pacing therapies may ular fibrillation; VT, ventricular tachycardia.
be efficacious and less painful than shocks. Finally, percutane-ous radiofrequency ablation may decrease the incidence of VTin selected patients.
(CPI/Guidant) may cause reprogramming of tachyarrhyth-mia therapies. In general, bradyarrhythmia functions arenot affected by magnet application to ICDs. Specific ICD responses to magnet application for various manufac- If the patient with multiple shocks has minimal symptoms, turers are noted in Table 2. If an attempt is made to inappropriate shocks should be considered. A differential inactivate an ICD with a magnet, the patient should not
diagnosis is included in Table 3. Stored intracardiac elec- be released until the status of the ICD is formally checked trograms and datalogs from the ICD are invaluable in de- with a programmer.
termining the cause of inappropriate shocks.
Table 2. ICD Response to Continuous Application of a Magnet
Tachycardia Therapy Response to
Tones Heard When Magnet Placed?
Response to Magnet?
None—device set to ignore magnet; Tone synchronized with QRS changing to tone synchronized with QRS— continuous tone—device off; tachycardia therapies active; continuous tone changing to tone synchronized with QRS—device active; no tone—device programmed to ignoremagnet Magnet rate (77–96 Intermedics (Guidant) None—device set to ignore magnet; If beeps heard, inhibited beeping—tachycardia therapies off Telectronics (St. Jude) Ventritex (St. Jude) If programmed to respond, inhibited ACC CURRENT JOURNAL REVIEW Sep/Oct 2001 Figure 2. Flow diagram for evaluation and treatment of the ICD patient who has received therapy. Abbreviations: ATP, antitachycardia pacing; EGM, electrocardiograms; EMI,
electromagnetic interference; SVT, supraventricular tachycardia. Notes: a-class I antiarrhythmics include quinidine, disopyramide, procainamide, mexiletine, propafenoneand flecainide; b-class III agents include sotalol and dofetilide; c-not programmable on all devices. Adapted with permission from ref. 2.
The most common cause of inappropriate shocks is SVT.
complete heart block. Maintenance of sinus rhythm can be Ventricular rate control should be immediately obtained achieved with antiarrhythmics, cardioversion or radiofre- with intravenous agents that may include beta-blockers, quency ablation. Reprogramming of the ICD may also re- diltiazem, digoxin or amiodarone, all of which may be duce inappropriate shocks. For example, an increase in the converted to oral form if needed on a chronic basis. In some VT detection rate may prevent a sinus tachycardia from cases, definitive ventricular rate control can be achieved triggering the device or addition of SVT discrimination only by ablation of the atrioventricular node to induce algorithms may suppress therapy in the presence of atrialfibrillation with a rapid ventricular response. Other SVT Table 3. Differential Diagnosis of Inappropriate Shocks
discrimination parameters may be programmed as outlinedin Table 4. Any reprogramming in ICD parameters should Atrial fibrillation be carefully reviewed to make sure that VT and VF detec- tion is not adversely affected.
Sinus tachycardia Oversensing causing double counting and inappropriate Atrial tachycardia therapy may be caused by T wave or diaphragmatic over- Reentrant supraventricular tachycardia sensing or counting of atrial and ventricular signals due to ventricular lead dislodgment or a separate bradycardia pac- Diaphragmatic/chest wall ing system. These can often be treated by reprogramming the ICD. If lead dislodgment is found, repositioning of the Lead dislodgment/double counting of atrium and ventricle lead will be necessary. If a pacemaker causes double count- External electromagnetic noise (alternators/welding/cautery/lithotripsy) ing, removal of the pacemaker and upgrading of the ICD Loose set screw/extendable lead screw system to incorporate bradyarrhythmia therapies should be Electromagnetic noise recorded on the sensing lead can ACC CURRENT JOURNAL REVIEW Sep/Oct 2001 Table 4. Detection Enhancements for Differentiation of SVT from VT
What It Does
Useful For
Suppresses therapy for tachyarrhythmias Atrial fibrillation Underdetection of VT with irregular rate; with variable V rate failure to suppress therapy or SVTswith regular V response Suppresses therapy for tachyarrhythmias Sinus tachycardia Underdetection of gradually accelerating that slowly accelerate VT or VT onset during sinustachycardia; failure to suppress therapyfor sudden onset SVTs Suppresses therapy for tachyarrhythmias Potentially useful for differentiation of Limited specificity with bundle branch with V EGM morphology similar to that narrow complex SVT from VT block; may prevent therapy for narrow Suppresses therapy for tachyarrhythmias Potentially useful for differentiation of Limited specificity with bundle branch with ventricular EGM morphology similar to that in sinus rhythm A rate-V rate relationship Suppresses therapy for tachyarrhythmias Atrial flutter and other SVTs with May delay therapy for VT with retrograde where A rate ⱖV rate regular ventricular response Certain patterns of A and V timing A activity falling in refractory period or associated with SVT suppress therapy farfield R waves detected on A channelcan confound algorithm Sustained rate duration Therapy for tachyarrhythmias finally Prevents indefinite inhibition of therapy Therapy will be eventually delivered if the delivered after this period of time, even for VT misdiagnosed as SVT SVT continues after sustained high rate if SVT discriminators are still met Note: some detection enhancements are available only in certain models of ICD. Abbreviations: A, atrial; EGM, electrogram; SVT, supraventricular tachycardia; V, ventricular; VT, ventricular tachycardia.
cause inappropriate therapy. The most common cause of Cambridge, MA: Blackwell Scientific Publications, 2001: this is a lead fracture which should be remedied by removal/ replacement of the fractured lead. Occasionally external Glikson M, Friedman PA. The implantable cardioverter-defibril- noise (e.g., high frequency electromagnetic signals from lator. Lancet 2001;357:1107–17.
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Ku¨hlkamp K, Do¨rnberger V, Mewis C, et al. Clinical experience magnets (typically found in theft detectors, motors, gen- with the new detection algorithms for atrial fibrillation of a erators, and audio speakers) can temporarily inhibit ICD defibrillator with dual chamber sensing and pacing. J Cardio- therapies for tachyarrhythmias. If an ICD patient is inad- vasc Electrophysiol 1999;10:905–15.
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Address correspondence and reprint requests to Kenneth A.
Strickberger SA, Man KC, Daoud EG, et al. A prospective eval- Ellenbogen, MD, Director, Clinical Cardiac Electrophysiology uation of catheter ablation of ventricular tachycardia as ad- Lab, Medical College of Virginia, Box 980053, Richmond, VA juvant therapy in patients with coronary artery disease and an ACC CURRENT JOURNAL REVIEW Sep/Oct 2001

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